What happens after two missed doses of Warfarin? Not much.

[QuincyRunner]

Last Sunday I decided to skip two doses of Warfarin to see how fast my INR dropped and how fast I could get it back up to therapeutic range (as a test in anticipation of non-cardiac surgery). My range is 2.5-3.5 (mitral valve) and I have historically been stable in that range with a daily Warfarin dosage of 7.5 mg. So, starting with an INR of 3.2 last Sunday I skipped my Sunday night and Monday night doses. On Tuesday night my INR was 1.6, a quicker drop than I had anticipated. That night I resumed Warfarin with 10 mg and on Wednesday night I took 12.5 mg, knowing well that by then my INR was probably getting close to 1. On Thursday night I took 15 mg and on Friday and Saturday nights I took my normal 7.5 mg. For the 5-day week I took 52.5 mg which is the same weekly dose as when I take 7.5 mg a day for seven days. Well, low and behold, my INR on Sunday was back up to 3.6 with no muss, no fuss. The upshot for me is that for minor surgeries that recommend an INR below 2, this would be a safe way to accomplish it without bridging or risk of bleeding. The risk of thrombosis is also low, especially since my INR drops quickly and rises quickly as well, leaving only a few days at most below therapeutic range. And if blood clots on a valve take upwards of a week to form, as I have read on this site as well as others, what's not to like?

 

[pellicle]

Hey that's good news, although I would question this bit

... if blood clots on a valve take upwards of a week to form

I've never read that, anywhere.

As I understood it there are two types of things you need to be aware of:

1. clots forming on a surface
2. clots forming in suspension within blood

the second type forms potentially every beat of the heart and this is caused by the opening / closing pressure jets potentially triggering thrombosis. These are then swept along and may snowball if not broken down in a timely fashion. This "snowballing" is of course reduced in speed by the presence of anticoagulation therapy. Accordingly I would avoid any strenuous activity (heavy weights, hard training) while the INR is below therapeutic.

None the less I am glad you have had a good result and that you're knowing yourself and how you react to ACT.

Best Wishes

 

[Chuck C]

Thanks for sharing your data.

with an INR of 3.2 last Sunday I skipped my Sunday night and Monday night doses. On Tuesday night my INR was 1.6, a quicker drop than I had anticipated.

This is not surprising to me with a two day hold. Holding just one day, I usually see my INR drop .8 to .9. We all differ in how quickly we clear warfarin, so it is a good thing to know how quickly your INR drops rather than estimate what your drop will be from studies on others.

It sounds like you have some useful data which will help you avoid being under target range longer than needed for your procedure. Best of luck with your procedure.

 

[tom in MO]

Last Sunday I decided to skip two doses of Warfarin to see how fast my INR dropped and how fast I could get it back up to therapeutic range (as a test in anticipation of non-cardiac surgery). My range is 2.5-3.5 (mitral valve) and I have historically been stable in that range with a daily Warfarin dosage of 7.5 mg. So, starting with an INR of 3.2 last Sunday I skipped my Sunday night and Monday night doses. On Tuesday night my INR was 1.6, a quicker drop than I had anticipated. That night I resumed Warfarin with 10 mg and on Wednesday night I took 12.5 mg, knowing well that by then my INR was probably getting close to 1. On Thursday night I took 15 mg and on Friday and Saturday nights I took my normal 7.5 mg. For the 5-day week I took 52.5 mg which is the same weekly dose as when I take 7.5 mg a day for seven days. Well, low and behold, my INR on Sunday was back up to 3.6 with no muss, no fuss. The upshot for me is that for minor surgeries that recommend an INR below 2, this would be a safe way to accomplish it without bridging or risk of bleeding. The risk of thrombosis is also low, especially since my INR drops quickly and rises quickly as well, leaving only a few days at most below therapeutic range. And if blood clots on a valve take upwards of a week to form, as I have read on this site as well as others, what's not to like?

Do you play Russian Roulette with a gun or just your valve? From the NIH:

Thrombosis of mechanical aortic valve prosthesis is a rare but life-threatening complication. In most reported cases, inadequate anticoagulation or cessation of anticoagulation is the cause of prosthesis thrombosis.​

I stopped warfarin and dropped my INR for surgery w/o bridging...My cardio said it was safe because of my valve - St. Jude and its position - aortic. With a mitral valve you have a higher INR because it is more susceptible to thrombosis formation than an aortic valve. I'd find a cardio you trust and let them make those decisions.

 

[Mister_James]

I do think there is a log linear curve with withholding warfarin. From 3.0 it's easy to get to 1.6 but it takes longer to drop from 1.6 to 1.0. This has to do with half lives of things...it is significant to get from 100 to 50 but it's not meaningful to drop from 4 to 2 even though the relationship is still the same.

 

[pellicle]

I do think there is a log linear curve with withholding warfarin.

unsurprisingly I've spent an amount of time on this. I would tend to agree but my experience is that its not symmetrical ... roll off is different to roll in. Both different non-linear curves.

I mean, from a laymans perspective.